Summary/Abstract Acute kidney injury (AKI) is a common problem and associated with increased morbidity and mortality and development of chronic kidney disease (CKD) and in some cases end stage renal disease (ESRD). There are no FDA approved drugs to prevent AKI, and this is in part related to systemic side effects of these drugs. In this application we propose two approaches to prevent AKI. Firstly, we propose the pre-emptive use of ex-vivo induced regulatory B cell infusion to prevent AKI. We have shown that isolated B cells, pretreated ex-vivo with IgM or CpG, develop into regulatory B cells (Bregs), which when intravenously infused into mice, 24 hours before renal ischemia, protect mice from renal ischemia induced AKI and we show that protection is mediated by inhibiting the ischemia induced inflammatory response (IIR) which is primarily responsible for AKI. We show that the infused Bregs interact and regulate in-vivo NKT-1 cell, which normally amplify the IIR. We would like to also examine how IgM or CpG pretreatments switch B cells into Bregs. Secondly, we propose that CpG ,when pre-emptively administered to mice, prevents AKI. Others have shown that CpG when administered 3 or 4 days or 1 hour before the ischemic event in murine hearts or brain, protects these mice from ischemia induced damage. CpG,when administered 1 hour before the ischemic event, protects by enhancing tolerance of non-immune cells (i.e cardiomyocytes, neurons) to ischemia induced cell injury/death. However, we do not understand how CpG protects against ischemic damage when given 3 or 4 days before ischemia and there are no studies on the protective effect of CpG in AKI. We propose that CpG when given at -3 or -4 days induces production of high in-vivo natural IgM, which we have shown is broadly anti-inflammatory and protects kidneys by inhibiting IIR. We would like, in this application, to investigate the mechanism for CpG induced protection and evaluate if CpG and Bregs, when combined is more protective. We will use two murine models of AKI i.e ischemia and LPS induced sepsis to determine if Bregs and/or CpG inhibit innate inflammation. This project has a good chance for translation into humans as CpG is currently used in vaccines and we induced ex- vivo human Bregs with IgM and CpG pretreatment. Both Bregs and/or CpG can be used to prevent AKI in high risk cardiac surgery and in deceased organ donors or recipients.